Output TAP files, and do some more tests.
authorSteinar H. Gunderson <sgunderson@bigfoot.com>
Thu, 2 May 2013 21:29:04 +0000 (23:29 +0200)
committerSteinar H. Gunderson <sgunderson@bigfoot.com>
Thu, 2 May 2013 21:29:04 +0000 (23:29 +0200)
decode.c

index 923913d..85872a0 100644 (file)
--- a/decode.c
+++ b/decode.c
@@ -1,4 +1,5 @@
 #include <stdio.h>
+#include <string.h>
 #include <math.h>
 #include <unistd.h>
 #include <assert.h>
@@ -7,11 +8,21 @@
 
 #define LANCZOS_RADIUS 30
 #define BUFSIZE 4096
-#define HYSTERESIS_LIMIT 1000
+#define HYSTERESIS_LIMIT 3000
 #define SAMPLE_RATE 44100
 #define C64_FREQUENCY 985248
 #define TAP_RESOLUTION 8
 
+#define SYNC_PULSE_LENGTH 380.0
+#define SYNC_TEST_TOLERANCE 1.10
+
+struct tap_header {
+       char identifier[12];
+       char version;
+       char reserved[3];
+       unsigned int data_len;
+};
+
 double sinc(double x)
 {
        if (fabs(x) < 1e-6) {
@@ -78,6 +89,11 @@ double find_zerocrossing(const std::vector<short> &pcm, int x)
        return 0.5f * (upper + lower);
 }
 
+struct pulse {
+       double time;  // in seconds from start
+       double len;   // in seconds
+};
+       
 int main(int argc, char **argv)
 {
        std::vector<short> pcm;
@@ -102,19 +118,22 @@ int main(int argc, char **argv)
        }
 #endif
 
-       std::vector<float> pulse_lengths;  // in seconds
+       std::vector<pulse> pulses;  // in seconds
 
        // Find the flanks.
        int last_bit = -1;
        double last_upflank = -1;
        int last_max_level = 0;
-       for (int i = 0; i < pcm.size(); ++i) {
+       for (unsigned i = 0; i < pcm.size(); ++i) {
                int bit = (pcm[i] > 0) ? 1 : 0;
                if (bit == 1 && last_bit == 0 && last_max_level > HYSTERESIS_LIMIT) {
                        // up-flank!
                        double t = find_zerocrossing(pcm, i - 1) * (1.0 / SAMPLE_RATE);
                        if (last_upflank > 0) {
-                               pulse_lengths.push_back(t - last_upflank);
+                               pulse p;
+                               p.time = t;
+                               p.len = t - last_upflank;
+                               pulses.push_back(p);
                        }
                        last_upflank = t;
                        last_max_level = 0;
@@ -123,24 +142,55 @@ int main(int argc, char **argv)
                last_bit = bit;
        }
 
-       // Calibrate on the first ~15k pulses (skip a few, just to be sure).
-       float calibration_factor = 1.0f;
-       if (pulse_lengths.size() < 20000) {
+       // Calibrate on the first ~25k pulses (skip a few, just to be sure).
+       double calibration_factor = 1.0f;
+       if (pulses.size() < 20000) {
                fprintf(stderr, "Too few pulses, not calibrating!\n");
        } else {
                double sum = 0.0;
-               for (int i = 1000; i < 16000; ++i) {
-                       sum += pulse_lengths[i];
+               for (int i = 1000; i < 26000; ++i) {
+                       sum += pulses[i].len;
                }
-               double mean_length = C64_FREQUENCY * sum / 15000.0f;
-               calibration_factor = 380.0 / mean_length;
+               double mean_length = C64_FREQUENCY * sum / 25000.0f;
+               calibration_factor = SYNC_PULSE_LENGTH / mean_length;
                fprintf(stderr, "Cycle length: %.2f -> 380.0 (change %+.2f%%)\n",
                        mean_length, 100.0 * (calibration_factor - 1.0));
+       
+               // Check for pulses outside +/- 10% (sign of misdetection).
+               for (int i = 1000; i < 25000; ++i) {
+                       double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
+                       if (cycles < SYNC_PULSE_LENGTH / SYNC_TEST_TOLERANCE || cycles > SYNC_PULSE_LENGTH * SYNC_TEST_TOLERANCE) {
+                               fprintf(stderr, "Sync cycle with upflank at %.6f was detected at %.0f cycles; misdetect?\n",
+                                       pulses[i].time, cycles);
+                       }
+               }
        }
 
-       for (int i = 0; i < pulse_lengths.size(); ++i) {
-               int len = lrintf(pulse_lengths[i] * calibration_factor * C64_FREQUENCY / TAP_RESOLUTION);
-               //fprintf(stderr, "length: %f (0x%x)\n", t - last_upflank, len);
-               printf("0x%x\n", len);
+       std::vector<char> tap_data;
+       for (unsigned i = 0; i < pulses.size(); ++i) {
+               double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
+               int len = lrintf(cycles / TAP_RESOLUTION);
+               if (i > 15000 && (cycles < 100 || cycles > 800)) {
+                       fprintf(stderr, "Cycle with upflank at %.6f was detected at %.0f cycles; misdetect?\n",
+                                       pulses[i].time, cycles);
+               }
+               if (len <= 255) {
+                       tap_data.push_back(len);
+               } else {
+                       int overflow_len = lrintf(cycles);
+                       tap_data.push_back(0);
+                       tap_data.push_back(overflow_len & 0xff);
+                       tap_data.push_back((overflow_len >> 8) & 0xff);
+                       tap_data.push_back(overflow_len >> 16);
+               }
        }
+
+       tap_header hdr;
+       memcpy(hdr.identifier, "C64-TAPE-RAW", 12);
+       hdr.version = 1;
+       hdr.reserved[0] = hdr.reserved[1] = hdr.reserved[2] = 0;
+       hdr.data_len = tap_data.size();
+
+       fwrite(&hdr, sizeof(hdr), 1, stdout);
+       fwrite(tap_data.data(), tap_data.size(), 1, stdout);
 }